Intake Manifold Benefits - Manifold Destiny

What's Better-A Dual-Plane Or A Single-Plane Manifold?

John Heida, owner of Speedway Testing is the guy responsible for the dyno pulls in our manifold test session. While John is a self-confessed NHRA class racer, he is also a self-proclaimed tinkerer. John points out that no matter what he tests, there's always something to learn.

The time has come to buy a new intake manifold for your hot rod. There are plenty of choices on the market: single-plane, dual-plane, dual four-barrel, three two-barrel, tunnel-ram, and so on. You've narrowed it down to a single carb intake. Single four-barrel manifolds come in two basic configurations: dual-plane and single-plane. Both designs have been around for years, and each has its own benefits. But which is better for your motor's combination? The answer is it depends. But let's back up a bit and see how the two manifold types differ.

Different StrokesFirst, let's look at the most common race manifold (which, obviously, is the single-plane). Generally speaking, a single-plane intake includes a large, centrally located plenum which has reasonably straight runners leading from the plenum to the port entries in the cylinder head. In a single-plane configuration, there is a large common plenum under the carburetor. According to the experts, this "common" plenum allows each runner and cylinder intake port combination to draw from all four of the carburetor venturis at wide-open throttle.

As the partially vaporized air-fuel mixture leaves the base of the carburetor venturis, it forms as four individual mixture streams. When each of the cylinders places a demand on the plenum chamber, these mixture streams (or in some cases, portions of the streams) physically bend in the direction of demanding runner-port entry. The mixture "streams" combine to form a single "mixture river" which flows into the runner, eventually feeding the cylinder which is making the demand.

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Here is the pair of HVH-Brodix manifolds we tested. As you can see, there's quite a bit of difference in the configuration of the manifolds. The dual-plane is likely very street-car friendly and will easily fit under most stock hoods. Meanwhile, the SP1 is a tall, race car configuration, geared more to a more radical combination. What's with the spacers? We also flogged various HVH Super Sucker and Street Sweeper spacer combinations on a variety of manifold types.

The beauty of a single-plane manifold configuration is that it allows each runner to withdraw a larger volume of air-fuel mixture during the available induction time span. Unfortunately, life isn't always simple-and neither are intake manifolds. As each cylinder withdraws a charge from the plenum, the "mixture streams" are forced to change direction constantly. Creating more havoc inside the manifold are pressure pulses which travel backward from the cylinder into the manifold runner and eventually into the plenum. And some engine combinations have more of this reverse pressure pulsation than others do. These constant directional changes in the plenum, along with pressure pulses, can create a healthy amount of turbulence inside the plenum.

Dual-plane manifolds, on the other hand, were used in great numbers on carbureted production engines. In these cases, low-rpm performance of the car was the primary concern. To enhance the low-rpm ability of the respective street car engines, a dual-plane manifold was almost always used. In essence this manifold is a two-in-one arrangement. Each half (or "plane") of the intake routes the air-fuel mixture from a separate plenum area to an individual group of cylinders (obviously, four cylinders in a V-8).

With each side of the intake separated from the other, individual intake runners are grouped so that 180 degrees of crank rotation separates the intake cycles of the cylinders fed by the same half of the manifold. Given the layout of the manifold, the runners can be (and, in practice, always are) long. Coupled with 180-degree separation of the cylinders, these manifolds, at least in theory, are best suited to engines which operate up to approximately 5,500 rpm. Of course, this also means that, in theory, this manifold configuration should be best used in a low-rpm, high-torque application.

Much For TheoryFrom our perspective, at least, we thought it would be interesting to compare two very good manifolds to see what the differences in dual- and single-plane manifolds really were. So we picked up the phone and called John Heida at Speedway Testing and posed the intake manifold question. Now, John flushes quite a few engines (drag race, street/strip, and street) through his dyno facility, and we thought he might have a perfect candidate for the test. He did. The small-block he had available was very typical of a solid, basic bracket engine. Specs for the engine are as follows:

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Intake Manifold Benefits - Manifold Destiny

John Heida, owner of Speedway Testing is the guy responsible for the dyno pulls in our manifold test session. While John is a self-confessed NHRA class racer, he is also a self-proclaimed tinkerer. John points out that no matter what he tests, there's always something to learn.

Here is the pair of HVH-Brodix manifolds we tested. As you can see, there's quite a bit of difference in the configuration of the manifolds. The dual-plane is likely very street-car friendly and will easily fit under most stock hoods. Meanwhile, the SP1 is a tall, race car configuration, geared more to a more radical combination. What's with the spacers? We also flogged various HVH Super Sucker and Street Sweeper spacer combinations on a variety of manifold types.

Here's an up-close look at the HVH-Brodix SP1. It's an impressive intake manifold right out of the box, and even on a relatively mild-cammed small-block, it almost approached the performance level of a well-sorted dual-plane.

Meanwhile, the king of the test was this manifold: the HVH-Brodix dual-plane. While it might look pedestrian, this manifold, when coupled with a special HVH "Street Sweeper" spacer, produced the most noteworthy and useable power and torque figures.

For this test, we ran the engine with the headers used on the car-a First-Generation Chevy II, but the test was accomplished without mufflers. An interesting aspect of Heida's Superflow Dyno facility is the special "fireplace" (visible aft of the engine). What's with that? Simple: John is prepared to test mufflers on both street and race engines.

Here's a look at the "Street Sweeper" spacer mentioned in the text. If you refer to the story, you'll see that this particular spacer helped to produce the strongest numbers in our test. In fact, it picked up our king-of-the-hill HVH-Brodix dual-plane by 6 hp and 9 lb-ft of torque.

Our tests were comprehensive. We actually ran four different intakes and a variety of spacers on the engine. It's also interesting to note that the engine in question works perfectly with unleaded pump gas, coupled with a very simple 780 Holley combination. The bottom line here is, for a street/strip Chevy, you don't really need exotic parts. Run-of-the-mill pieces work just fine. Just keep in mind there's power in intake manifolds, particularly if you select the right intake for the application.

When you flip the "Street Sweeper" over, you can see that it's not a common, garden-variety carb spacer. This spacer is engineered to work with dual-plane intakes, hence the specialized machining on the bottom side.